Ferrite circulators have a wide variety of uses in commercial and military, space and terrestrial, and low and high power applications. A waveguide circulator may be implemented in a variety of applications, including but not limited to low noise amplifier (LNA) redundancy switches, T/R modules, isolators for high power sources, and switch matrices. One important application for such waveguide circulators is in space, especially in satellites where extreme reliability is essential and where size and weight are very important. Ferrite circulators are desirable for these applications due to their high reliability, as there are no moving parts required. This is a significant advantage over mechanical switching devices. In most of the applications for waveguide switching and non-switching circulators, small size, low mass, and low insertion loss are significant qualities.
A commonly used type of waveguide circulator has three waveguide arms arranged at 120° and meeting in a common junction. This common junction is loaded with a non-reciprocal material such as ferrite. When a magnetizing field is created in this ferrite element, a gyromagnetic effect is created that can be used for switching the microwave signal from one waveguide arm to another. By reversing the direction of the magnetizing field, the direction of switching between the waveguide arms is reversed. Thus, a switching circulator is functionally equivalent to a fixed-bias circulator but has a selectable direction of circulation. Radio frequency (RF) energy can be routed with low insertion loss from one waveguide arm to either of the two output arms. If one of the waveguide arms is terminated in a matched load, then the circulator acts as an isolator, with high loss in one direction of propagation and low loss in the other direction.